Territorial?

MY BEARDED DRAGON CACTUS IS ABOUT 4 MONTHS OLD AND WE ARE STILL UNSURE IF IT IS A BOY OR GIRL BUT I REFER TO IT AS HE LOL.

Cactus was fine when we first got him, when we would pick him up out of his terrarium he would try to run and we would give him a minute. Put our hand down, and scoop him slowly so he wouldn't be afraid. He was getting better to where he would just let us pick him up from underneath, but for some reason he started running again. But now, he is not just running, he is opening his mouth and hissing when we even try to get close to him. I am not sure what is causing this behavior, we are not reaching over top of him, or grabbing him tightly or anything... We have been keeping our hand low and coming underneath him to pick him up..
Once he is out of his terrarium, he is totally fine! He runs and explores and doesn't open his mouth or hiss at all, and he will let us pick him up, he will even crawl on us and fall asleep. It seems he is getting really territorial and I have stopped picking him up because I do not want to get bit and become afraid of him..
We have two hiding spots in his terrarium and a basking area, I don't really think the way we have his place set up is what is causing this.
Also, we were taking him out during feeing and to spend time with him, but now we have just started feeding him in his terrarium because he is getting so mad..
I really thought we were taking good care of him, please tell me what you think!

How long have you had him? Mine was very aggressive when we got him as well --- it took months to get him to quit running hissing biting etc............. but I worked w/ him every day - at one point I was wearing a glove just so I could pick him up and get him used to being picked up- I hand fed him had my hand in the tank as much as possible - etc -- I would hand feed him worms maybe place a piece of clothing in the tank or fleece blanket w/ your smell on it in his hide - it will get him used to your smell - I never let mine run outside the tank as when I took him out of his tank to hold just out side of it he would get a black beard not real black but enough to know he was stressed out -- let him acclimate to his surroundings and keep working w/ him --- some are very stubborn as mine was but he is calm now and no more of the aggressive behavior
Karrie